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Characterisation and utilisation of microbes in the production of fish sauce and paste

Lubbe, Beatrix (2000-12)

Thesis (MSc Food Sc )--Stellenbosch University, 2000.

Thesis

ENGLISH ABSTRACT: Fermented fish products are popular food products mainly consumed and
produced in Southeast Asia. These products are not produced in South Africa,
and those available to the public are imported. The main action during the
production and fermentation of this sort of product, is that of proteolysis, either by
the bacteria or enzymes naturally present in the fish.
The prevalent microbes present in six fermented fish samples from
Bangkok (Thailand) and seven from Khon Kaen (Thailand), were determined, and
using numerical methods, clustered into similarity groups using the calculated
dendrogram .distance (Do) technique to determine their relation to reference
strains. Forty-seven different bacterial strains were isolated, but no yeasts,
moulds or lactic acid bacteria were found. Five Gram-negative, oxidase-positive
species, five different Staphylococcus species and nine different
endospore-forming species of the genus Bacillus, were isolated and identified
using the API systems. The data indicated that members of the genus Bacillus
were the prevalent organisms in all the products examined.
The isolates were also scanned for general enzyme activity using the API
Zym technology, and the production of proteases was investigated using the
Standard Methods Caseinate and the Universal Protease Substrate methods. It
was found that most of the isolated organisms produced protease, which is of
major importance in the production of fermented fish products.
Proteolytic cultures from the fermented fish products, as well as lactic acid
starters, were used in the production of a fermented fresh water fish product.
Production parameters including: glucose, inoculum, moisture content and
incubation time, were evaluated in order to select optimum fermentation
conditions. Fermentation efficiency was determined by measuring the final pH,
titratable acid and the free amino nitrogen content. Optimum efficiency was
obtained with 5% (w/w) added glucose at a moisture level of 150 ml water per 100
g fish.
A factorial design (3 x 3 x 3) was used to indicate viable trends to facilitate
optimisation of the fermentation process. The main effects, two-factor and
three-factor interactions were calculated. Optimum trends obtained were a glucose concentration of 5% (wlw) , inoculum concentration of 1x10⁸ kve.ml ̄ ¹, an
incubation period of 15 days and temperature of 30°C. Three lactic acid starters
(226 - Lactobacillus plantarum, 140 - Lactococcus diacetylactis and 407 -
Pediococcus cerevisiae) were selected as they produced some of the best
fermentation results and are safe to use in food. It was found that a combination
of all three strains (226, 140 and 407) yielded the best results.
By using the above parameters, an acceptable product was produced in terms of
consistency, colour and aroma. Further studies need to be conducted to optimise
the safety of the product as well as the flavour, both chemically and sensorically
optimisation of the product.